Identification of three LRR-RKs involved in perception of root meristem growth factor in Arabidopsis

Abstract

A peptide hormone, root meristem growth factor (RGF), regulates root meristem development through the PLETHORA (PLT) stem cell transcription factor pathway, but it remains to be uncovered how extracellular RGF signals are transduced to the nucleus. Here we identified, using a combination of a custom-made receptor kinase (RK) expression library and exhaustive photoaffinity labeling, three leucine-rich repeat RKs (LRR-RKs) that directly interact with RGF peptides in Arabidopsis. These three LRR-RKs, which we named RGFR1, RGFR2, and RGFR3, are expressed in root tissues including the proximal meristem, the elongation zone, and the differentiation zone. The triple rgfr mutant was insensitive to externally applied RGF peptide and displayed a short root phenotype accompanied by a considerable decrease in meristematic cell number. In addition, PLT1 and PLT2 protein gradients, observed as a gradual gradient decreasing toward the elongation zone from the stem cell area in wild type, steeply declined at the root tip in the triple mutant. Because RGF peptides have been shown to create a diffusion-based concentration gradient extending from the stem cell area, our results strongly suggest that RGFRs mediate the transformation of an RGF peptide gradient into a PLT protein gradient in the proximal meristem, thereby acting as key regulators of root meristem development.peptide hormone | receptor | plant | stem cell | sulfated peptide

RGF1 INSENSITIVE 1 to 5, a group of LRR receptor-like kinases, are essential for the perception of root meristem growth factor 1 in Arabidopsis thaliana

“…Therefore, we believe that RGIs, at least RGI1, qualify as the receptors of RGF1. This conclusion is consistent with recent independent studies from two other research groups [55,56]. Matsubayashi's group used a photoaffinity approach and identified three RGF1 receptors in Arabidopsis [55], which are identical to our RGI1 to RGI3.…”

“…This conclusion is consistent with recent independent studies from two other research groups [55,56]. Matsubayashi's group used a photoaffinity approach and identified three RGF1 receptors in Arabidopsis [55], which are identical to our RGI1 to RGI3. On the other hand, Chai's group identified the same 5 RGF1 receptors as we show here based on the presence of conserved RXR and RXGG signature motifs in the extracellular domains of these receptors [56].…”

Signature motif-guided identification of receptors for peptide hormones essential for root meristem growth

“…During the preparation of the manuscript, three LRRRLKs, corresponding to RGFRs 1, 3 and 4 identified in the current study, were reported to be involved in RGF perception [30]. In addition, an accompanying study [31] identified the same five LRR-RLKs as receptors for RGFs by using a completely different approach from ours, further supporting the validity of our biochemical assay for matching of receptors and their ligands.…”

“…For coexpression, resuspended bacteria containing different constructs were mixed with equal OD 600 of 0.4. After 46 h, 10 nM RGF1 or 1 µM PSK [30] was infiltrated into tobacco leaves, while double-distilled water was infiltrated as mock. All leaves were harvested after 2 h of infiltration.…”

Peptide signaling in plants: finding partners is the key

“…Just before the pair of papers were published in Cell Research, another group [12], using RLK expression library and photoaffinity-labeled RGF1, identified three RLKs of the same family to function as RGF receptors. Following the identification of the RGF peptides [4], Matsubayashi group began to explore the possibility of RLK family members as RGF receptors.…”